(1) Field of the Invention
The present invention relates to torque down control apparatus and method for an automotive vehicle and particularly relates to the torque down control apparatus and method which reduce a drive torque by means of a dynamic power under a predetermined condition.
(2) Description of Related Art
A Japanese Patent No. 3517847 issued on Feb. 6, 2004 exemplifies a previously proposed torque down control apparatus in which, when an engine drive force is recovered by means of such a traction control that an engine drive force is suppressed in order for a slip quantity of drive wheels to become equal to a target slip quantity, an accelerator pedal is returned to an original no depression force application state (so-called, a release state or accelerator OFF state) in a midway through the recovery and, at this time, the recovery of the engine drive force is limited to a torque reduction direction.
The torque down control is useful not only during an execution of traction control but also in a case where an automotive vehicle is first traveled from a stopped state. In addition, the torque down control is carried out to prevent an abrupt recovery of the drive force when one of the following cases is eliminated. That is to say, the cases include a case where an interlock failure of an automatic transmission occurs, a case when the engine becomes stall with any one or more of frictional engagement elements released, and a case when a neutral failure occurs.
In the automatic transmission, clutches and brakes are provided in a transmission mechanism including gears as its rotary transmission elements and combinations of engagement and release of these elements achieve a plurality of shift stages. For example, if such a, so-called, interlock failure state that frictional engagement elements such as clutches and brakes are the combination of the engagement and release different from a normal case thereof occurs, the vehicle cannot move since a revolution output of the automatic transmission is not generated in spite of the fact that the revolution from the engine is inputted in the automatic transmission. A vehicle driver, in many cases, once returns the accelerator pedal to the no-depression force application state (accelerator OFF state) from the accelerator ON state and again depresses the accelerator pedal (accelerator ON state). Actually, this often eliminates the interlock and the vehicle, in many cases, becomes a movement enabled state (the vehicle can be traveled).
However, in a case where the vehicle driver again depresses the accelerator pedal (accelerator ON state), the vehicle often carries out an abrupt recovery of the drive force when the interlock is eliminated.
As a countermeasure of the occurrence of the abrupt recovery described above, it can be thought that, in a case of the interlock failure, such a torque down control that an engine torque limitation (or regulation) value is set which suppresses an upper limitation of the engine drive force, the engine drive force is gradually recovered in an increase direction, and the recovery of the engine drive force is limited to a torque decrease direction when the accelerator pedal is returned to no depression force application state (the release state).